This invention relates to hydraulic clutch actuator assemblies for motor vehicle clutches and, more particularly, to a slave cylinder of the so-called xe2x80x9cconcentricxe2x80x9d type having an improved two-piece housing which facilitates the reduction in the size, weight and cost of the overall actuator assembly.
It is known to use a hydraulic actuator assembly consisting of a master cylinder and a slave cylinder to operate the clutch of a motor vehicle. The piston of the master cylinder is mechanically connected to the clutch pedal to move fluid through a conduit through the slave cylinder where a second piston is displaced to operate the clutch. When the pedal is released, bias springs in the clutch force the second piston back to its original position returning fluid from the slave cylinder to the master cylinder.
It is known to design slave cylinders in such a way that they may be concentrically mounted relative to the transmission input shaft within a bell-shaped housing placed between the engine and the transmission. This is generally illustrated for example in assignee""s U.S. Pat. Nos. 4,585,106; 4,585,107; 4,585,108; 4,585,109; 4,609,087; 4,264,290; 4,660,694; 4,684,003; 4,687,084 and 4,708,228.
The prior art concentric slave cylinders have been either a one-piece construction or a two-piece construction. The housing in the concentric slave cylinder consists generally of two concentric cylindrical portions having a common base flange in the case of a one-piece construction, or commonly joined base flanges in the case of a two-piece construction. In either case the inner wall of the outer cylindrical portion is spaced from the outer wall of the inner cylindrical portion to define an annular fluid chamber which, when the assembly is completed by addition of an annular piston and an annular piston seal, defines the fluid volume for the concentric slave cylinder.
The prior art one-piece constructions, while relatively inexpensive, suffer from the disadvantage that the size of the fluid chamber must be relatively large. Specifically, the annular spacing of the walls must to be large enough to permit the entry of a tool to finish the inside surfaces to the degree necessary for proper functioning of the piston and piston seal.
The prior art two-piece constructions, while allowing the provision of smaller chamber sizes and thereby smaller concentric slave cylinder and smaller master cylinder sizes, have been relatively expensive to manufacture because of the requirements for close tolerances and costly primary and secondary finishing operations with respect to each piece of the two-part construction.
The principle objective of the present invention is to provide a concentric slave cylinder for motor vehicle clutches in which the fluid volumes in the master and slave cylinders are significantly reduced and the cost of providing the cylinder is reduced.
In general, this is accomplished by fabricating the concentric slave cylinder housing in two separate pieces, including an inner cylindrical member having a base flange and an outer cylindrical member having a base flange, and forming one of the members as an injection molded polymer member. This arrangement retains the advantage of the two-piece construction with respect to a small fluid chamber while eliminating finishing operations with respect to the polymer housing member and thereby reducing the overall cost of the slave cylinder.
In one embodiment of the invention, both the inner and outer cylindrical members are formed as an injection molded polymer member. In a second embodiment, the inner cylindrical member is formed as a cold formed metallic member and the outer cylindrical member is formed as an injection molded polymer member. In a third embodiment, the outer member is formed as a cold formed metallic member and the inner cylindrical member is formed as an injection molded polymer member.
In all of the embodiments, the inner and outer cylindrical members have integral base flanges which are positioned in confronting relation in the assembled housing and which are suitably secured together to provide the cylinder housing assembly.
In all of the embodiments, the use of the two-piece construction allows the annular gap or spacing between the two cylindrical portions to be minimized. For example, a gap on the order of about 3 or 4 mm. may be provided utilizing the two-piece construction as compared to a minimum 6 mm. gap when utilizing a one-piece construction.
Further, in all of the embodiments, the use of at least one injection molded polymer member significantly reduces the overall cost of the housing assembly since the injection molded polymer member, as compared to a cast metallic member, eliminates the need for the secondary finishing operations required in the cast metallic member to provide the surface finish required for proper functioning of the piston and seal in the annular chamber.
The details of all embodiments are hereinafter described to the degree necessary to permit persons of ordinary skill in the clutch hydraulics technologies to make and use same.